1. Field
Exemplary embodiments of the present invention relate to a semiconductor design technology and, more particularly, to an internal voltage generation circuit for generating a pumping voltage.
2. Description of the Related Art
In general, semiconductor devices such as double data rate synchronous DRAM (DDR SDRAM) generate internal voltages having various voltage levels, which are supplied to internal circuits. Semiconductor devices accomplish this by using power from external controllers. The internal voltages include those that are generated through down conversion operations and pumping operations. Internal voltages generated through down conversion operations include, for example, core voltages used to set data levels in the semiconductor memory devices and precharge voltages used to precharge bit lines. The internal voltages generated through pumping operations include pumping voltages applied to gates of cell transistors and substrate bias voltages applied to substrates of cell transistors.
As the integration of semiconductor devices is increased, a design rule of a sub-micron grade or less is applied to the design of internal circuits. In order to drive such a fine circuit at high speed, the voltage level of power applied to the circuit is lowered. Accordingly, the voltage supplied to semiconductor devices is also lowered. In recent years, much effort has been given to generate internal voltages using low supply voltages.
Pumping voltage generation circuits of internal voltage generation circuits are described below as an example.
FIG. 1 is a diagram illustrating a conventional pumping voltage generation circuit.
Referring to FIG. 1, the pumping voltage generation circuit has first to N-th pumping units 110_1 to 110_N for generating pumping voltages by pumping an input voltage.
The first pumping unit 110_1 pumps the input voltage received through an input terminal IN. The first pumping unit 110_1 pumps the input voltage in response to positive/negative clock signals CLK and /CLK and outputs the pumping voltage to a first output terminal OUT_1. Although not illustrated in FIG. 1 for simplicity, the first pumping unit 110_1 is coupled to the second pumping unit. The second pumping unit receives the pumping voltage from the first pumping unit 110_1, pumps the received voltage, and outputs the pumping voltage to a second output terminal (not illustrated). Next, the N-th pumping unit 110_N receives a voltage output from a pumping unit at a previous stage, pumps the received voltage, and outputs the pumping voltage to a final output terminal OUT_FIN.
A brief circuit operation of the pumping voltage generation circuit is described below with reference to FIG. 1. It is assumed that the number of pumping units is 9, i.e., N=9, for convenience. That is, the pumping voltage generation circuit may include first to ninth pumping units. Furthermore, it is assumed that the input voltage of 2 V is applied to the input terminal IN and each of the first to ninth pumping units performs a pumping operation with 2 V.
First, the first pumping unit 110_1 receives the input voltage of 2 V and performs a pumping operation when the positive/negative clock signals CLK and /CLK are toggled. The voltage level of the first output terminal OUT_1 is gradually raised up to 4 V through the pumping operation. The second pumping unit receives a voltage output through the first output terminal OUT_1 of the first pumping unit 110_1 and performs a pumping operation when the positive/negative clock signals CLK/CLK are toggled. Likewise, the ninth pumping unit performs a pumping operation. As a result, the voltage level of the final output terminal OUT_FIN may be pumped up to 20 V.
In order to obtain the pumping voltage of 20 V using the input voltage of 2 V, nine pumping units are required. For example, a scenario in which the input voltage is set to 12 V and a pumping voltage of 20 V is generated will be discussed. In this case, only four pumping units are required to generate the pumping voltage of 20 V. However, a breakdown voltage of the first pumping unit 110_1 needs to be 12 V or more. For example, if the first pumping unit 110_1 has a breakdown voltage of about 2 V, operation of the pumping voltage generation circuit is impossible. When the breakdown voltage of the first pumping unit 110_1 is set high, however, the size of the first pumping unit 110_1 needs to be large. This means that the size of the pumping voltage generation circuit is increased, which undesirable as the trend is to continue decreasing the amount of chip area consumed.